Medical devices are sterilized before being used in hospitals, physicians' offices, and other medical facilities. Steam, heat, ethylene oxide, and hydrogen peroxide are commonly used as sterilizing agents.
It is standard practice to include a sterility indicator in a load of articles that are to be sterilized in a sterilizer. The sterility indicator provides a measure of whether the sterilization process was effective in sterilizing the articles in a particular load. If the sterilization process was not effective, as indicated by the sterility indicator, the load of equipment may be rejected for use.
Biological indicators are generally recognized as reliable sterility indicators. The biological indicator includes a carrier that has been inoculated with spores or other microorganisms. Spores are often utilized as indicator organisms in biological indicators, because spores are generally more resistant to sterilization than other microorganisms.
The biological indicator is placed into the sterilizer with the equipment to be sterilized. At the end of the sterilization process, the biological indicator is removed from the sterilizer, and the carrier is immersed in a sterile culture medium. The culture medium and carrier are incubated for a predetermined time at an appropriate temperature. At the end of the incubation period, it is determined whether any microorganisms have grown in the growth medium. If there is no growth of microorganisms in the growth medium, it is assumed that the equipment in the sterilizer has been properly sterilized. If microorganism growth is observed, the sterilization process was not effective, and the articles in the sterilizer may be rejected for use.
The growth of microorganisms may be determined through a signal such as the generation of turbidity in the growth medium or a color change in a pH indicator due to a pH change resulting from byproducts of cell growth in the medium. Biological indicators are described, for example, in Burnham et al. (U.S. Pat. No. 5,552,320) and Hendricks et al. (U.S. Pat. No. 6,436,659), both of which are incorporated herein by reference in their entirety.
Although biological indicators are accurate indicators for the effectiveness of the sterilization cycle, at least 24-48 hours are required to obtain results from the biological indicators. The equipment that was exposed to the sterilization procedure is sometimes kept in quarantine until the results from the biological indicator are available. Medical equipment is expensive, and storage space in medical facilities is limited. Some hospitals therefore use the equipment before the results are available. Storing quarantined medical equipment is not an efficient use of resources. There is a need for a rapid test for determining the effectiveness of a sterilization process.
Foltz et al. (U.S. Pat. No. 6,355,448) describe a method for determining the effectiveness of a sterilization process by measuring the deactivation of enzymes rather than spores. It is stated that the enzyme test procedure requires only a few minutes rather than the several days that are required to obtain results from biological indicators.
The use of a plurality of enzymes rather than a single enzyme was disclosed, for example, by Burnham et al. in U.S. Pat. No. 5,486,459 and Hendricks et al. in U.S. Pat. No. 6,528,277. A plurality of enzymes was believed to better mimic the response of a microorganism to a sterilization process than a single enzyme. Enzymes may react differently than spores or bacteria to the sterilization process, however.
Feltner et al. (U.S. 2003/0064427) describe a method of rapidly determining the effectiveness of a sterilization process by measuring the amount of dipicolinic acid (DPA) that is released during the sterilization process. The spores that are generally used as indicator organisms in sterilization processes contain approximately 10-15 weight % DPA. The DPA is normally present in the cortex and coat of the spore in the form of calcium dipicolinate. Feltner et al. found that DPA was released from the spores when the spores were deactivated.
Feltner et al. determined the concentration of DPA in the solution surrounding the spores through spectroscopic analysis at a wavelength of approximately 545 nm or by derivative ultraviolet spectroscopic analysis. The sensitivity of the analysis could be enhanced by adding a lanthanide salt and by using ultraviolet light for excitation and visible light for emission.
The analysis method of Feltner requires expensive instrumentation and complex data analysis. The detection limit was not given.
There is a need for a method for rapidly measuring the effectiveness of sterilization without expensive instrumentation and complex data analysis methods.